1. Field of the Invention
This invention relates to a device for installing a tire-wheel assembly onto a wheel balancer for measuring and correcting a rotating unbalance of the tire-wheel assembly.
2. Description of the Related Art
As shown in FIG. 7, the conventional device 1 for installing a tire-wheel assembly onto a wheel balancer comprises a wheel receiving member 3, a tapered cone 4 of a frustoconical shape, a wheel pushing member of a frustoconical shape and a female screw member 6, which are concentrically attached to a rotating shaft 2 extending from a main body of a wheel balancer (not shown). The wheel receiving member 3 is constructed by integrally uniting a disc-contacting portion 3a with a cup-shaped base portion 3b, in which a bottom of the base portion 3b is concentrically fixed to the rotating shaft 2 passing therethrough and the disc-contacting portion 3a extends outward from the base portion 3b in a direction perpendicular to the rotating shaft 2. Moreover, the disc-contacting portion 3a has a smooth metal surface as shown in FIG. 8a or is provided at its smooth surface with a plurality of fine and shallow circular grooves 9 as shown in FIG. 8b. A coil-shaped spring 8 is disposed in a cavity 7 of the wheel receiving member 3 between the bottom of the base portion 3b and the tapered cone 4. The tapered cone 4 is slidably moved on the rotating shaft 2 inside the wheel receiving member 3 when a pushing force is applied to the tapered cone 4 from a right side in FIG. 7.
After a disc portion of a tire-wheel assembly (not shown) is mounted onto the wheel receiving member 3, the wheel pushing member 5 is slidably loaded on the rotating shaft 2 from a top 2a thereof and moved toward the wheel receiving member 3 by the female screw member 6 engaging with male threads formed on the outer surface of the rotating shaft 2 over a given region ranging from the top 2a in the longitudinal direction through a handle portion 6a attached to the female screw member 6 to fix the disc portion between the wheel receiving member 3 and the wheel pushing member 5.
Thus, the tire-wheel assembly is mounted onto the installing device 1 in which the rotating shaft 2 is projected sideways from the balancing body of the wheel balancer. In this case, the disc portion of the wheel is first contacted with the tapered cone 4 at a position corresponding to a center hole of the disc portion by pushing the disc portion of the wheel toward the wheel receiving member 3 through the wheel pushing member 5 and the female screw member 6. At this stage, the tire-wheel assembly takes an unstable posture against the installing device because the position of center of gravity in the axial direction of the tire-wheel assembly is usually offset toward a front side of the. Also the tire-wheel assembly is biased downward against the rotating shaft 2 due to the fact that the inclined outer surface of the tapered cone 4 is downward to the right.
As the pushing force is applied to the disc portion from the front side of the tire-wheel assembly by moving the wheel pushing member 5 while manipulating the handle 6a of the female screw member 6, the inner peripheral face of the center hole of the disc portion slides on the inclined surface of the tapered cone 4, whereby the disc portion of the tire-wheel assembly is stopped at an adequate position on the inclined surface of the tapered cone 4. When the pushing force is further applied to the disc portion through the female screw member 6, the spring 8 is compressed on the rotating shaft 2 toward the bottom of the base portion 3b to closely adhere the back surface of the disc portion to the disc-contacting portion 3a of the wheel receiving member 3, whereby the mounting of the tire-wheel assembly onto the installing device 1 is completed.
After mounting of the tire-wheel assembly onto the installing device 1, any unbalance of the tire-wheel assembly is measured by actuating the wheel balancer and a balancing weight is attached to a balancing position of the wheel indicated by the balancer to correct the unbalance to zero. When such a corrected tire-wheel assembly is detached from the installing device 1 and again mounted onto the installing device in the same manner as described above, the unbalance appears and the unbalacing quantity of about 10-20 g (grams) frequently measured.
As a result of various investigations on a cause of poor reproducibility in the measurement of unbalance and correction thereof, the following has been confirmed. That is, when the tire-wheel assembly is mounted onto the installing device 1, it rides on the tapered cone 4 at the unstable posture as previously mentioned. When the tire-wheel assembly is pushed toward the wheel receiving member 3 through the wheel pushing member 5 and female screw member 6 at such a state, the inner peripheral face of the center hole in the disc portion is located on the tapered cone 4 at a somewhat inclined state with respect to a plane perpendicular to the axis of the tapered cone 4, or a part of the rear surface of the disc portion facing the wheel receiving member 3 is contacted with the disc-contacting portion 3a of the wheel receiving member 3 to complete the mounting of the tire-wheel assembly. That is, it has been confirmed that the remaining part of the rear surface of the disc portion located opposite by 180.degree. to the part closely contacting with the disc-contacting portion 3a is at a floating state separated from the disc-contacting portion 3a. Such a slant mounting of the tire-wheel assembly with respect to the installing device 1 results in dynamic unbalance, while the mounting at a biased state results in static unbalance, which degrade naturally the reproducibility of the aforementioned unbalance correction.